1. Field of the Invention
The present invention relates to a coagulating sedimentation processing apparatus for applying coagulating sedimentation processing to suspension or the like.
2. Description of the Related Art
Conventionally, water or waste water which is emitted or discharged from a waste-water plant, for example, is sent to a coagulating sedimentation processing apparatus as suspension, and coagulating sedimentation processing is applied to the water in the coagulating sedimentation processing apparatus, so that suspended material in the suspension is separated from the water.
In this case, the arrangement is such that the suspension is supplied to the sedimentation tank, additive such as inorganic coagulant, polymeric coagulant or the like is added to the suspension to form flocks, the flocks are bulked up so as to become suspended material, and the suspended material is separated from the suspension and is settled on a bottom of the sedimentation tank. For this reason, the arrangement is such that the suspension is supplied to an upper portion of a tubular mixing chamber which is arranged at a center of the sedimentation tank, additive is added to the suspension during the time in which suspension moves down within the mixing chamber, and is mixed with the suspension to form mixing liquid, and the mixing liquid flows radially outwardly from a lower end of the mixing chamber and is moved upwardly outwardly of the mixing chamber.
The flocks are bulked out at a position outward the mixing chamber, and form sludge which is sedimented downwardly. Meanwhile, cleaned processed water is moved upwardly and flows out from an overflow section.
However, the flocks which are formed in the mixing liquid are not dense, and particulate diameters of the flocks per se are different from each other. Accordingly, when uneven or non-uniform flow is generated within the sedimentation tank by flow of the mixing liquid within the mixing chamber and by wind on a surface of the sedimentation tank, the flocks having small particulate diameters are moved upwardly to a location adjacent to the liquid surface, and flow out together with the processed water from the overflow section.
In view of the above, a coagulating sedimentation processing apparatus has been proposed in which distributors are rotated within the sedimentation tank such that uneven flow is not generated in the mixing liquid which is moved upwardly outwardly of the mixing chamber, and even or uniform flow is generated within the sedimentation tank.
FIG. 2 of the attached drawings is a schematic view of the prior art or conventional coagulating sedimentation processing apparatus.
In FIG. 2, the reference numeral 11 denotes a sedimentation tank which receives therein suspension. A clean layer 11a principally consisting of processed water, a coagulated flock layer 11b mainly consisting of flocks and a concentrated sludge layer 11c mainly consisting of sludge are formed in order from a liquid level of the sedimentation tank 11 to a bottom thereof.
Further, the reference numeral 12 denotes a line for supplying the suspension; 13, a pump which is arranged in the line 12; and 15, a mixing chamber whose upper end opens. The suspension is supplied to an upper portion of the mixing chamber 15 through the line 12. The mixing chamber 15 is suspended at a center of the sedimentation tank 11, and is rotated by a drive unit 16 which is arranged at the upper end of the mixing chamber 15. A rake arm 18 is provided at a bottom of the sedimentation tank 11. The rake arm 18 is mounted on a lower end of the mixing chamber 15 and is rotated together with the mixing chamber 15.
Meanwhile, various kinds of additives, for example, inorganic coagulant, polymeric coagulant, neutralizer and the like are supplied to the upper portion and the lower portion of the mixing chamber 15 through lines 19 and 20, and are added to the suspension. In this connection, the reference numerals 21 and 22 denote pumps which are arranged respectively in the lines 19 and 20.
Moreover, a sludge discharge line 23 and a sludge returning line 24 are arranged at a bottom of the sedimentation tank 11. A part of sludge can be discharged to the outside of the system through the sludge discharge line 23. The remaining part of sludge can be returned through the sludge returning line 24, and can be supplied to the upper portion of the mixing chamber 15. In this connection, the reference numeral 25 denotes a pump which is arranged in the sludge discharge line 23; and 26, a pump which is arranged in the sludge returning line 24.
Furthermore, a mixer 31 in the form of stirring blades is suspended within the mixing chamber 15. The mixer 31 is rotatively driven by a drive unit 32 which is arranged at the upper end of the mixer 31 so that the suspension, the returned sludge and the additive within the mixing chamber 15 are mixed with each other.
A plurality of tubular distributors 35 extend radially at the lower end of the mixing chamber 15. A plurality of jetting ports 36 are formed in each of the distributors 35 so as to open downwardly. In this connection, the reference numeral 38 denotes a surface detector which is arranged within the clean layer 11a; and 39, an overflow section which is formed at an upper end of the sedimentation tank 11.
The coagulating sedimentation processing apparatus arranged as described above operates as follows:
Suspension is supplied to the mixing chamber 15 through the line 12, the additive is supplied to the mixing chamber 15 through the lines 19 and 20, and the returned sludge is supplied to the mixing chamber 15 through the sludge returning line 24. They are agitated or stirred within the mixing chamber 15 by the mixer 31 to form mixing liquid. The mixing liquid is urged radially outwardly of the distributors 35 by a centrifugal force in keeping with rotation of the mixing chamber 15, and is jetted into the coagulating flock layer 11b from the jetting ports 36.
The mixing liquid which is jetted into the coagulating flock layer 11b forms initial flocks at that time. The initial flocks move upwardly while riding the uniform flow of the mixing liquid. The initial flocks are caught or trapped within the coagulating flock layer 11b, and are formed into bulked and dense flocks.
Meanwhile, the clean processed liquid is further raised within the sedimentation tank 11 to form the clean layer 11a. Further, a part of the flocks within the coagulating flock layer 11b is moved downwardly within the sedimentation tank 11 to form sludge, to thereby form the concentrated sludge layer 11c.
Accordingly, the sludge sedimented on the bottom of the sedimentation tank 11 is condensed by the rake arm 18 which is rotated together with the mixing chamber 15. A part of the condensed sludge is discharged to the outside of the system through the sludge discharge line 23, while the remainder of the condensed sludge forms returned sludge which is again supplied to the mixing chamber 15 through the sludge returning line 24.
During this time, the surface height of the clean layer 11a and the surface height of the coagulating flock layer 11b are detected by the surface detector 38. The pump 25 is driven such that the surfaces are not placed upwardly beyond the predetermined heights, and the sludge is discharged through the sludge discharge line 23.
In this manner, the suspended material within the suspension is separated, and the cleaned processed water flows out or is discharged from the overflow section 39.
Since the aforesaid prior art coagulating sedimentation processing apparatus is arranged such that the mixing liquid is jetted downwardly from the jetting ports 36 of the distributors 35, it is possible to form a uniform flow of the mixing liquid within the sedimentation tank 11. However, turbulent flow is generated, by the jetted mixing liquid, in the concentrated sludge layer 11c within a range of from 50 [cm] to 150 [cm] from the lower end of the distributors 35.
In this case, there is a problem that a quantity of the concentrated sludge layer 11c is substantially reduced, and the concentration of the sludge is also reduced.
Moreover, in the aforementioned prior art coagulating sedimentation processing apparatus, the mixing liquid within the mixing chamber 15 is jetted into the coagulating flock layer 11b from the jetting ports 36 of the respective distributors 35. However, the initial flocks which are formed at that time are deposited within the distributors 35 and are adhered to the jetting ports 36. The sludge within the coagulation flock layer 11b is adhered to the jetting ports 36 so that the jetting ports 36 are blocked.
There is a problem that, since, in this case, the mixing liquid is jetted only from the jetting ports 36 which are not blocked, uneven or non-uniform flow is generated within the sedimentation tank 11.